As far as the video card goes, your machine is an Athlon XP so probably AGP 2x or 4x. You can get decent used video cards for that incredibly cheap on eBay or other places for under $40, like an nVidia 6 series with 128 MB RAM. Stick with nVidia cards since ATI cards didn’t play well with AMD machines back then.
His motherboard has a PCI-E slot....you can get cards at a reasonable price though.,